Broadband access technologies such as cable, fiber optic, and wireless have made rapid progress in recent years. Recently there has been a convergence of voice and data networks which is due in part to US deregulation of the telecommunications industry. In order to stay competitive, companies offering broadband access technologies need to support voice, video, and other high-bandwidth applications over their local access networks. For networks that use a shared access medium to communicate between subscribers and the service provider (e.g., cable networks, wireless networks, etc.), providing reliable high-quality voice/video communication over such networks is not an easy task.
One type of broadband access technology relates to cable modem networks. A cable modem network or “cable plant” employs cable modems, which are an improvement of conventional PC data modems and provide high speed connectivity. Cable modems are therefore instrumental in transforming the cable system into a full service provider of video, voice and data telecommunications services.
FIG. 1 shows a block diagram of a conventional two-way hybrid fiber-coaxial (HFC) cable network 100. As shown in FIG. 1, the cable network 100 includes a Head End complex 102 typically configured to service about 40,000 homes. The Head End complex 102 may include a plurality of components and/or systems (not shown) such as, for example, a Head End, a super Head End, a hub, a primary hub, a second hub, etc. Additionally, as shown in FIG. 1, the Head End complex 102 typically includes a Cable Modem Termination System (CMTS). Primary functions of the CMTS include (1) receiving data inputs from external sources 100 and converting the data for transmission over the cable plant; (2) providing appropriate Media Access Control (MAC) level packet headers for data received by the cable system, and (3) modulating and demodulating the data to and from the cable network. Typically, the Head End complex 102 is configured to provide a communication interface between nodes (e.g. cable modems) in the cable network and external networks such as, for example, the Internet. The cable modems typically reside at the subscriber premises 110A-D.
The Head End Complex 102 is typically connected to one or more fiber nodes 106 in the cable network. Each fiber node is, in turn, configured to service one or more subscriber groups 110. Each subscriber group typically comprises about 500 to 2000 households. A primary function of the fiber nodes 106 is to provide an optical-electronic signal interface between the Head End Complex 102 and the plurality of cable modems residing at the plurality of subscriber groups 110.
In order for data to be able to be transmitted effectively over a wide area network such as HFC or other broadband computer networks, a common standard for data transmission is typically adopted by network providers. A commonly used and well known standard for transmission of data or other information over HFC networks is the Data Over Cable System Interface Specification (DOCSIS). The DOCSIS standard has been publicly presented by Cable Television Laboratories, Inc. (Louisville, Colo.), in a document entitled, DOCSIS 2.0 RF Interface Specification (document control number SP-RFIv2.0-I04-030730, Jul. 30, 2003). That document is incorporated herein by reference for all purposes.
Communication between the Head End Complex 102 and fiber node 106a is typically implemented using modulated optical signals which travel over fiber optic cables. More specifically, during the transmission of modulated optical signals, multiple optical frequencies are modulated with data and transmitted over optical fibers such as, for example, optical fiber links 105a and 105b of FIG. 1, which are typically referred to as “RF fibers”. As shown in FIG. 1, the modulated optical signals transmitted from the Head End Complex 102 eventually terminate at the fiber node 106a. The fiber nodes maintain the signal modulation while converting from the fiber media to the coax media and back.
Each of the fiber nodes 106 is connected by a coaxial cable 107 to a respective group of cable modems residing at subscriber premises 110A-D. According to the DOCSIS standard, specific frequency ranges are used for transmitting downstream information from the CMTS to the cable modems, and other specific frequency ranges are used for transmitting upstream information from the cable modems to the CMTS.
In order to allow the cable modems to transmit data to the CMTS, the cable modems share one or more upstream channels within that domain. Access to the upstream channel is controlled using a time division multiplexing (TDM) approach. Such an implementation requires that the CMTS and all cable modems sharing an upstream channel within a particular domain have a common concept of time so that when the CMTS tells a particular cable modem to transmit data at time T, the cable modem understands what to do. “Time” in this context may be tracked using a counter, commonly referred to as a timestamp counter, which, according to conventional implementations is a 32-bit counter that increments by one every clock pulse.
Typically, digital data on upstream and downstream channels of the cable network is carried over radio frequency (“RF”) carrier signals. Cable modems convert digital data to a modulated RF signal for upstream transmission and convert downstream RF signal to digital form. The conversion is done at a subscriber's facility. At a Cable Modem Termination System (“CMTS”), located at a Head End Complex of the cable network, the conversions are reversed. The CMTS converts downstream digital data to a modulated RF signal, which is carried over the fiber and coaxial lines to the subscriber premises. The cable modem then demodulates the RF signal and feeds the digital data to a computer. On the return path, the digital data is fed to the cable modem (from an associated PC for example), which converts it to a modulated RF signal. Once the CMTS receives the upstream RF signal, it demodulates it and transmits the digital data to an external source.
FIG. 2 shows an example of a portion of a conventional cable network 200. As illustrated in FIG. 2, the CMTS 210 may include a plurality of line cards 202A, 202B, 202C. Each line card may include a downstream port (not shown) for transmitting information from the CMTS to the cable modems, and a plurality of upstream ports (e.g., 206A) for transmitting information from the cable modems to the CMTS. As illustrated in FIG. 2, each upstream port (e.g., Port A1) is physically configured to communicate with a respective group of cable modems (e.g., Group A 260a), which typically are located within a common physical region or location. Thus, for example, the cable modems in Group A 260a are physically configured to communicate with the CMTS via upstream Port A1, cable modems in Group B 260b are physically configured to communicate with the CMTS via upstream Port A2, cable modems in Group C 260c are physically configured to communicate with the CMTS via upstream Port B1, etc.
In conventional CMTS configurations such as those illustrated, for example, in FIG. 2, the line cards within the CMTS are not interconnected in a manner which allows for cable modems from different groups to “talk” to different line cards. Additionally, according to conventional line card configurations, there is no interconnection between each of the different upstream ports on a particular line card. Thus, for example, as illustrated in FIG. 2, the cable modems within Group A 260a are physically configured to communicate with the CMTS 210 via upstream Port A1, cable modems within Group B 260b are physically configured to communicate with the CMTS 210 via upstream Port A2. Because of this configuration constraint, problems may occur during a failure of one or more components associated with a particular line card. For example, if there is a failure a component of the upstream channel associated with Port A1, the cable modems of Group A 260a will be unable to communicate with the CMTS. Typically, in order to remedy such a problem, the entire line card will have to be replaced, resulting in service disruptions for all cable modem groups associated with that line card.
Another problem with conventional line card configurations is that the lack of interconnection between upstream ports also limits the availability to perform load balancing between various upstream ports on a given line card. Thus, for example, when new subscribers are added to a region where all cable modems (CMs) are physically connected to a fixed upstream port, there is no way to improve upstream bandwidth efficiency unless the connections from CMs to the fixed US port are physically reconfigured.
Accordingly, it will be appreciated that there exists a continual need to improve access network and line card configurations in order to provide improved network capabilities and performance.